undef-ing an active subroutine

perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

Hi all,

Is there a clever way to undef an "active" subroutine? I'd like to do this:

sub foo {
  undef &foo;
  ...
}
[download]

I find it curious that undef-ing is not permitted but that this is allowed:

sub foo {
  *{foo} = sub { warn "second foo" };
  ...
}
[download]

In my case the sub I want to undef is an AUTOLOAD sub, and I'd want to remove it from the symbol table so it can't get called again.

Comment on undef-ing an active subroutine Select or Download Code

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Re: undef-ing an active subroutine by ikegami (Patriarch) on Feb 01, 2010 at 15:20 UTC
So deactivate it: `>perl -wle"sub real_AUTOLOAD { undef &AUTOLOAD; } sub AUTOLOAD { print + 'A'; goto &real_AUTOLOAD } f() for 1..2;" A Undefined subroutine &main::f called at -e line 1.` [download] Getting rid of the whole glob works too: `>perl -wle"sub AUTOLOAD { print 'A'; undef *AUTOLOAD; } f() for 1..2;" A Undefined subroutine &main::f called at -e line 1.` [download]	[reply] [d/l] [select]
Re: undef-ing an active subroutine by moritz (Cardinal) on Feb 01, 2010 at 15:29 UTC
You can delete it from the symbol table: `use strict; use warnings; sub foo { delete $::{foo}; print "alive\n"; } foo(); eval "foo()" or die $@;` [download] Note that I put the second call to foo into an eval because Perl looks up the symbol at compile type. Perl 6 - links to (nearly) everything that is Perl 6.	[reply] [d/l]
Re: undef-ing an active subroutine by kennethk (Abbot) on Feb 01, 2010 at 15:36 UTC
Along with the lovely suggestions from ikegami and moritz, you can use caller to make the deletion less fragile if you move your subroutine about: `#!/usr/bin/perl use strict; use warnings; foo(); eval{foo()} or warn $@; print "Done\n"; sub foo { { no strict 'refs'; undef *{(caller(0))[3]}; } print "foo was called\n"; }` [download]	[reply] [d/l]
Re: undef-ing an active subroutine by aquarium (Curate) on Feb 01, 2010 at 22:47 UTC
unless there's a good reason it's probably safer coding to bind to new code that returns undef, instead of deleting a sub. the hardest line to type correctly is: stty erase ^H	[reply]